New modes of continuous renal replacement therapy using a refiltering technique to reduce micronutrient loss

INTRODUCTION: Micronutrient depletion is a major drawback of high-dose continuous renal replacement therapy (CRRT). We tested two novel CRRT modes, double-filtration hemofiltration (DHF) and dialysate-recycling hemodiafiltration (DHDF), aimed at reducing micronutrient loss while maintaining a high clearance rate of midsized solutes comparable to that of high-volume hemofiltration (HVHF). METHODS: Forty patients with renal failure requiring CRRT were randomly assigned to receive predilutional standard-volume hemofiltration (SVHF, effluent rate 35 mL/kg/h), predilutional HVHF (100 mL/kg/h), DHF (35 mL/kg/h), and DHDF (30 mL/kg/h). In the two novel modes of CRRT, part of the high-volume primary effluent fluid produced by a high-flux filter (AV600S) was refiltered by two low-flux filters (15 L) for recycling as replacement fluid in DHF and dialysate in DHDF, while the remainder was discarded as final effluent fluid. Specimens were collected for measurement of trace elements, folic acid, amino acids (AAs), β2-microglobulin, cystatin C, and creatinine and for calculation of solute clearance. FINDINGS: The clearance of 17 AAs, phosphorus, folic acid, copper, and zinc by DHF and DHDF was much lower than that by HVHF and comparable to that by SVHF. The estimated amount of AA loss by SVHF, HVHF, DHF, and DHDF was 10.3 (7.2-13.4) g/d, 22.1 (17.8-24.0) g/d, 10.6 (8.6-14.0) g/d, and 10.0 (8.6-11.4) g/d, respectively. Clearance of cystatin C and β2-microglobulin by DHF and DHDF was much greater than that by SVHF and equal to that by HVHF. DISCUSSION: Compared to HVHF, DHF, and DHDF have an equal capacity for removal of large solutes but show substantially reduced micronutrient loss.